1. Field of the Invention
The present invention relates to a vehicle battery""s open circuit voltage estimating method and a system therefor for estimating an open circuit voltage of a vehicle-borne battery which supplies electric power to vehicle-borne loads.
2. Description of the Related Art
An open circuit voltage of a battery is obtained by measuring a terminal voltage (i.e. disconnected voltage) in a disconnected state of the battery in an equilibrium state. The open circuit voltage of a battery indicates a charged state of the battery and is the most important for grasping how much of the electricity is charged (i.e. the charged state) in the battery aboard the vehicle.
Generally, when the discharged electricity flows from the battery, the terminal voltage of the battery drops according to the current. Reversely, when the charging current flows, the terminal voltage rises. For example, the voltage drop at the discharge is due to an impedance (i.e. combined resistance) of the battery and consists of a voltage drop (IR loss) due to a pure resistance (ohmic resistance) based on the structure of the battery, a voltage drop due to the activation polarization of the polarization resistance component based on the chemical reaction, and a voltage drop due to the concentration polarization of the polarization resistance component based on the chemical reaction.
The IR loss becomes 0 at the same time of the discharge current becoming 0. The voltage drop due to the activation polarization becomes 0 relatively in a short time. Though the voltage drop due to the concentration polarization lowers according to decrease of the discharge current, this voltage drop remains relatively long time after the discharge current has become 0 since the dissolution of the concentration polarization by diffusion of the electrolyte needs relatively long time. The above state of the voltage drop due to the discharge remaining after the discharge is called a non-equilibrium state. The terminal voltage (the disconnected voltage) of the battery measured in a disconnected state in the above state is to be different from a disconnected voltage (an open circuit voltage) in the equilibrium state wherein the voltage drop due to the discharge has dissolved (i.e. disappeared) and, that is, changes toward the open circuit voltage as time goes on after the discharge stopped.
Here, the disconnected voltage of the battery which rose by the flow of the charging current is different from the open circuit voltage since the risen voltage due to the concentration polarization remains relatively long time similarly to the case of the discharge.
Generally, the terminal voltage of the battery changes toward the open circuit voltage as shown in FIG. 3 after the completion of the charge and as shown in FIG. 9 after the completion of the discharge. The time to reach the equilibrium state, in a case of the charge completion for example, is shorter when the temperature is higher as shown in FIG. 10.
Therefore, the disconnected voltage measured at 24 hours after the completion of the discharge, when the equilibrium state can be expected, is generally considered to be the open circuit voltage.
With respect to the above method, however, the disconnected voltage to be the open circuit voltage is measured after waiting until the equilibrium state. If the discharge or the charge is carried out before passing such a time, there is no chance to measure the disconnected voltage until a definite time has passed.
And, since the time until the equilibrium state is affected by the temperature, if the disconnected voltage is measured and considered to be the open circuit voltage after a fixed time has passed without considering the ambient temperature, the measured disconnected voltage should vary. This causes an error and requires a correction due to temperature.
An object of the present invention is to provide a vehicle battery""s open circuit voltage estimating method and a system therefor which can relatively correctly estimate an open circuit voltage of a battery on a vehicle within a relatively short period after the completion of the charge or discharge also without a correction due to temperature.
The present inventions with the following first to fourth aspects relate to the vehicle battery""s open circuit voltage estimating method, and the inventions with the following fifth to eight aspects relate to the vehicle battery""s open circuit voltage estimating system. Each invention has a basis that the disconnected voltage of the battery after the charge or discharge changes asymptotically along a predetermined power approximate expression toward a predetermined voltage which can be estimated as an open circuit voltage.
In order to achieve the above object, as a first aspect of the present invention, a vehicle battery""s open circuit voltage estimating method for estimating an open circuit voltage of a vehicle-borne battery supplying electric power to vehicle-borne loads comprises the steps of: measuring a disconnected voltage of the battery multiple times in a definite period of time after a predetermined period of time after completion of charge or discharge of the battery; determining a power approximate expression having a negative power number by using a difference value of the measured disconnected voltage and an assumed open circuit voltage; repeating the determination of the power approximate expression by updating the assumed open circuit voltage until the power number of the determined power approximate expression becomes xe2x88x920.5 or about xe2x88x920.5; and estimating the assumed open circuit voltage to be the open circuit voltage when the power number becomes xe2x88x920.5 or about xe2x88x920.5.
According to the first aspect of the present invention, in a vehicle battery""s open circuit voltage estimating method for estimating an open circuit voltage of a vehicle-borne battery supplying electric power to vehicle-borne loads, a disconnected voltage of the battery is measured multiple times in a definite period of time after a predetermined period of time after completion of charge or discharge of the battery. A power approximate expression having a negative power number is determined by using a difference value of the measured disconnected voltage and an assumed open circuit voltage. The determination of the power approximate expression is repeated by updating the assumed open circuit voltage until the power number of the determined power approximate expression becomes xe2x88x920.5 or about xe2x88x920.5, and the assumed open circuit voltage is estimated to be the open circuit voltage when the power number becomes xe2x88x920.5 or about xe2x88x920.5. Therefore, an asymptote of the power approximate expression not changing due to the temperature can be estimated to be the open circuit voltage by measuring the disconnected voltage of the battery in a relatively short time after completion of the charge or the discharge of the battery. Therefore, a vehicle battery""s open circuit voltage estimating method, which can relatively correctly estimate the open circuit voltage of the battery in a relatively short time after completion of the charge or the discharge of the battery without a temperature correction, can be provided.
As a second aspect of the present invention, based on the first aspect, the power approximate expression is given by a xcex1xc2x7tD with time t, an unknown coefficient xcex1, and an unknown negative power number D, when the disconnected voltage is measured after completion of the charge.
According to the second aspect of the present invention, the power approximate expression is given by xcex1xc2x7tD with time t, an unknown coefficient xcex1, and an unknown negative power number D, when the disconnected voltage is measured after completion of the charge. And, the assumed open circuit voltage is estimated to be the open circuit voltage when the power number becomes xe2x88x920.5 or about xe2x88x920.5. Therefore, an asymptote of the power approximate expression not changing due to the temperature can be estimated to be the open circuit voltage by measuring the disconnected voltage of the battery in a relatively short time after completion of the charge of the battery. Therefore, a vehicle battery""s open circuit voltage estimating method, which can estimate the open circuit voltage of the battery in a relatively short time after completion of the charge of the battery without a temperature correction, can be provided.
As a third aspect of the present invention, based on the first aspect, the difference value for determining the power approximate expression is an absolute value obtained by subtracting the assumed open circuit voltage from the measured disconnected voltage when the disconnected voltage is measured after completion of the discharge, and the power approximate expression is given by xcex1xc2x7tD with time t, an unknown coefficient xcex1, and an unknown negative power number D.
According to the third aspect, the difference value for determining the power approximate expression is an absolute value obtained by subtracting the assumed open circuit voltage from the measured disconnected voltage when the disconnected voltage is measured after completion of the discharge, and the power approximate expression is given by xcex1xc2x7tD with time t, an unknown coefficient xcex1, and an unknown negative power number D. And, the assumed open circuit voltage is estimated to be the open circuit voltage when the power number becomes xe2x88x920.5 or about xe2x88x920.5. Therefore, an asymptote of the power approximate expression not changing due to the temperature can be estimated to be the open circuit voltage by measuring the disconnected voltage of the battery in a relatively short time after completion of the discharge of the battery. Therefore, a vehicle battery""s open circuit voltage estimating method, which can estimate the open circuit voltage of the battery in a relatively short time after completion of the discharge of the battery without a temperature correction, can be provided.
As a fourth aspect of the present invention, based on the second or third aspect, the power number D of the power approximate expression is determined by a regression computation processing by using a plurality of measured disconnected voltages and corresponding times from the completion of the charge or the discharge.
According to the forth aspect, the power number D of the power approximate expression is determined by a regression computation processing by using a plurality of measured disconnected voltages and corresponding times from the completion of the charge or the discharge. Accordingly, even if the power number D of the power approximate expression xcex1xc2x7tD does not become xe2x88x920.5, the assumed open circuit voltage can be estimated to be the open circuit voltage when the determination of the power approximate expression is repeated by a predetermined number of times. Therefore, an asymptote of the power approximate expression not changing due to the temperature can be accurately estimated to be the open circuit voltage by measuring the disconnected voltages of the battery in a relatively short time after completion of the charge or the discharge of the battery. Therefore, a vehicle battery""s open circuit voltage estimating method, which can relatively correctly estimate the open circuit voltage of the battery in a relatively short time after completion of the charge or the discharge of the battery without a temperature correction, can be provided.
As a fifth aspect of the present invention, a vehicle battery""s open circuit voltage estimating system for estimating an open circuit voltage of a vehicle-borne battery z supplying electric power to vehicle-borne loads comprises: a disconnected voltage measuring means for measuring a disconnected voltage of the battery multiple times in a definite period of time after a predetermined period of time after completion of charge or discharge of the battery; an approximate expression determining means for determining a power approximate expression having a negative power number by using a difference value of the measured disconnected voltage and an assumed open circuit voltage; and an arithmetic operation controlling means for making the approximate expression determining means update the assumed open circuit voltage and determine the power approximate expression repeatedly until the power number of the determined power approximate expression becomes xe2x88x920.5 or about xe2x88x920.5, wherein the assumed open circuit voltage is estimated to be the open circuit voltage when the power number becomes xe2x88x920.5 or about xe2x88x920.5.
According to the fifth aspect, a disconnected voltage measuring means measures a disconnected voltage of the battery multiple times in a definite period of time after a predetermined period of time after completion of charge or discharge of the battery. An approximate expression determining means determines a power approximate expression having a negative power number by using a difference value of the measured disconnected voltage and an assumed open circuit voltage. And, an arithmetic operation controlling means makes the approximate expression determining means update the assumed open circuit voltage and determine the power approximate expression repeatedly until the power number of the determined power approximate expression becomes xe2x88x920.5 or about xe2x88x920.5, and the assumed open circuit voltage is estimated to be the open circuit voltage when the power number becomes xe2x88x920.5 or about xe2x88x920.5. Therefore, a vehicle battery""s open circuit voltage estimating system, which can relatively correctly estimate the open circuit voltage of the battery in a relatively short time after completion of the charge or the discharge of the battery without a temperature correction, can be provided.
As a sixth aspect of the present invention, based on the fifth aspect, the power approximate expression is given by xcex1xc2x7tD with time t, an unknown coefficient xcex1, and an unknown negative power number D, when the disconnected voltage is measured after completion of the charge.
According to the sixth aspect of the present invention, the power approximate expression is given by xcex1xc2x7tD with time t, an unknown coefficient xcex1, and an unknown negative power number D, when the disconnected voltage is measured after completion of the charge. And, the assumed open circuit voltage is estimated to be the open circuit voltage when the power number becomes xe2x88x920.5 or about xe2x88x920.5. Therefore, an asymptote of the power approximate expression not changing due to the temperature can be estimated to be the open circuit voltage by measuring the disconnected voltage of the battery in a relatively short time after completion of the charge of the battery. Therefore, a vehicle battery""s open circuit voltage estimating system, which can estimate the open circuit voltage of the battery in a relatively short time after completion of the charge of the battery without a temperature correction, can be provided.
As a seventh aspect of the present invention, based on the fifth aspect, the difference value for determining the power approximate expression is an absolute value obtained by subtracting the assumed open circuit voltage from the measured disconnected voltage when the disconnected voltage is measured after completion of the discharge, and the power approximate expression is given by xcex1xc2x7tD with time t, an unknown coefficient xcex1, and an unknown negative power number D.
According to the seventh aspect, the difference value for determining the power approximate expression is an absolute value obtained by subtracting the assumed open circuit voltage from the measured disconnected voltage when the disconnected voltage is measured after completion of the discharge, and the power approximate expression is given by xcex1xc2x7tD with time t, an unknown coefficient xcex1, and an unknown negative power number D. And, the assumed open circuit voltage is estimated to be the open circuit voltage when the power number becomes xe2x88x920.5 or about xe2x88x920.5. Therefore, an asymptote of the power approximate expression not changing due to the temperature can be estimated to be the open circuit voltage by measuring the disconnected voltage of the battery in a relatively short time after completion of the discharge of the battery. Therefore, a vehicle battery""s open circuit voltage estimating system, which can estimate the open circuit voltage of the battery in a relatively short time after completion of the discharge of the battery without a temperature correction, can be provided.
As an eighth aspect of the present invention, based on the sixth or seventh aspect, the power number D of the power approximate expression is determined by a regression computation processing by using a plurality of measured disconnected voltages and corresponding times from the completion of the charge or the discharge.
According to the eighth aspect, the power number D of the power approximate expression is determined by a regression computation processing by using a plurality of measured disconnected voltages and corresponding times from the completion of the charge or the discharge. Accordingly, even if the power number D of the power approximate expression xcex1xc2x7tD does not become xe2x88x920.5, the assumed open circuit voltage can be estimated to be the open circuit voltage when the determination of the power approximate expression is repeated by a predetermined number of times. Therefore, an asymptote of the power approximate expression not changing due to the temperature can be accurately estimated to be the open circuit voltage by measuring the disconnected voltages of the battery in a relatively short time after completion of the charge or the discharge of the battery. Therefore, a vehicle battery""s open circuit voltage estimating system, which can relatively correctly estimate the open circuit voltage of the battery in a relatively short time after completion of the charge or the discharge of the battery without a temperature correction, can be provided.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.